The present invention relates generally to bias current setting apparatuses in magnetic recording and reproducing apparatuses. More particularly, the invention relates to an apparatus which automatically sets the bias current which is most suitable for recording on a magnetic recording medium used in a magnetic recording and reproducing apparatus.
In recent years, much progress has been made in research on and development of magnetic materials for magnetic tapes, and various kinds of magnetic tapes are being sold on the market. For example, there are at present magnetic tapes of classes called normal tapes, which have existed for some time, ferrichrome tapes, chrome tapes, and metal tapes, this classification being by the kind of magnetic material. These various kinds of tapes, however, have respectively different characteristics, whereby the most suitable bias current values for recording audio signals on these tapes are also respectively different. Furthermore, even among tapes of the same kind, the most suitable bias current value differs also depending on differences such as difference in thickness of the magnetic medium and differnce in the state of contact between the magnetic head and the tape.
For this reason, in order to accomplish good recording on a tape being used by causing that tape to amply exhibit its characteristics, irrespective of the kind of that tape, the bias current value most suitable for recording on that tape being used must be variably set.
Accordingly, there has heretofore been a system wherein the bias current is variably set by recording a signal of a specific frequency, thereafter reproducing this signal, operating a servo-motor in response to the level of the resulting reproduced output, and driving a variable resistor by means of the servo-motor. However, since a mechanical system is used in this known device, there arise problems when devices for purposes such as distortion factor and recording reference level correction are added, examples of such problems being the elaborate scale and nature of the entire device, high price, and the requirement of a long time for setting the most suitable bias current value.